With reference to FIG. 7, a description will be made about a conventional directional control valve assembly 100. FIG. 7 is a cross-sectional view of the conventional directional control valve assembly.
The conventional directional control valve assembly 60 is provided with a directional control valve 10 as a main valve, a check valve 20 for controlling a flow rate of pressure oil to be allowed to pass through the directional control valve 10, and a control means for controlling the check valve 20.
The directional control valve 10 is a spool valve, and is a spring-centered three-position valve. Formed in a valve body 61 of the directional control valve 10 are a supply port 12, first and second reservoir ports 13A, 13B, first and second I/O ports 14A,14B, a supply passage 15 extending from the supply port 12, and first and second branch passages 16A, 16B diverged from the supply passage 15.
The three valve positions of the directional control valve 10 include a neutral position, a first position and a second position. At the neutral position, the directional control valve 10 cuts off communication between the first branch passage 16A and the first I/O port 14A and also cuts off communication between the second I/O port 14B and the second branch passage 16B. At the first valve position, the directional control valve 10 communicates the first branch passage 16A and the first I/O port 14A but cuts off the communication between the second I/O port 14B and the second branch passage 16B to bring the second I/O port 14B into communication with the second reservoir port 13B. At the second valve position, the directional control valve 10 communicates the second branch passage and the second I/O port but cuts off the communication between the first I/O port 14A and the first branch passage 16A to bring the first I/O port 14A into communication with the first reservoir port 13A.
The check valve 20 is a spring-return valve, which is arranged to be capable of permitting or cutting off communication between a divergence portion 17, where the first and second branch passages 16A, 16B are diverged from the supply passage 15, and the supply passage 15 and to limit a flow of pressure oil between the supply passage 15 and the divergence portion 17 of the first and second branch passages 16A,16B to a direction that the flow is directed from the supply passage 15 toward the divergence portion 17.
The control means is provided with a pressure chamber 24 and a control valve 25. The pressure chamber 24 also serves as a spring chamber for a return spring 23 of the check valve 20, and can apply a pressure to a valve element 21 of the check valve 20 in a same direction as a biasing force by the return spring 23. The control valve 25 has a first port 31 interconnected with the divergence portion 17 via the second branch passage 16b and passages 62,63, a second port 32 interconnected with the pressure chamber 24 via a passage 64, and a spool 26 formed to be capable of permitting and cutting off communication between the first and second ports 31,32 and changing an opening degree of the communication.
The control means also has an oil chamber 39 formed in an outer peripheral wall of the valve element 21 of the check valve 20, an annular cutout 65 formed in the valve body 61 and being open to the pressure chamber 24 formed in the valve body 61, and a control slot 41 interconnecting these oil chamber 39 and annular cutout 65 with each other. Also arranged are an intra-valve-element passage 42 and au auxiliary check valve 43. The intra-valve-element passage 42 is formed inside the valve element 21 of the check valve 20, and is open at an end portion of the valve element 21, said end portion facing the supply passage 15, and also at the outer peripheral wall of the valve element 21, said outer peripheral wall facing the oil chamber 39. The auxiliary check valve 43 is arranged on the intra-valve-element passage 42, and allows pressure oil of a preset pressure or higher to flow from the supply passage 15 into the intra-valve-element passage 42.
The conventional directional control valve 60 is further provided with a protective member 66 and a rectifying member 67. The protective member 66 prevents positional displacements of the return spring 23 by flows of pressure oil that occur between the pressure chamber 24 and the second port 32. The rectifying member 67 straightens up each flow between the pressure chamber 24 and the second port 32.
Directional control valve assemblies of this kind include one disclosed in Patent Document 1.    Patent Document 1: JP-A-2006-017273